Update the PR template for latest 'additional documentation' enhancem…

…ents

- Clarify the ephemerality of links

Signed-off-by: Sascha Grunert <[email protected]>

.github/PULL_REQUEST_TEMPLATE.md

@@ -47,8 +47,15 @@ Enter your extended release note in the block below. If the PR requires addition
 
 <!--
 This section can be blank if this pull request does not require a release note.
-Please use the following format for linking documentation or pass the
-section below:
+
+When adding links which point to resources within git repositories, like
+KEPs or supporting documentation, please reference a specific commit and avoid
+linking directly to the master branch. This ensures that links reference a
+specific point in time, rather than a document that may change over time.
+
+See here for guidance on getting permanent links to files: https://help.github.com/en/articles/getting-permanent-links-to-files
+
+Please use the following format for linking documentation:
 - [KEP]: <link>
 - [Usage]: <link>
 - [Other doc]: <link>